Siemens PLC PID Problem

dutchkg

Member
Join Date
Jul 2008
Location
Kragujevac
Posts
1
Hy all,
I know that this is an easy one for You pros, but its giving me a headache. I will try to keep it short, but explain all in the same time. I'm using Siemens S7-200 CPU 224XP and STEP 7-MicroWIN V4.0.0.81 to make my programs. I have been working on several programs and everything went fine. Now I have to make program to control water level using PID (a must) and I'm stuck.
Water level - in volts: 1V for empty and 10V for full tank (linear change). Motor 0-5V to fill my tank. I made an ON-OFF program - works fine, but when I started with PID :sick:. I made PID with PID Wizard and set it up like: Low/High Range for the Loop Setpoint - 0.0/100.0; Gain - 1.0; Integral Time - 10.00 min; Sample Time - 1.0 sec; Derivative Time - 0.00min; Loop Input Low/High - 3200/32000 (to match 1-10V; is this correct?); Loop Output Low/High - 0/16000. Everything else is set as default.
Since I can't connect the PLC with tank at this time, I have to simulate water level so I use AC0 as input in PLC, where I increase and decrease its value with tasters (it is a discrete change but I think it does not change the process?!?). The Setpoint is set to 0.75 (75% of full tank is desired), and the output is at AQW0 (where I will put pump later on) where I measure the voltage with voltmeter. I have tree problems:
1. When I start the PLC, AC0 is 0, but AQW0 is 0 also (it should turn on and start the pump). When I increase AC0 to around 25000 (75% of full tank) and then decrease it, my pump starts to work. Why is that? Is there something wrong and how do I fix this? I want to measure the water level, as soon as I turn PLC ON, and if it's lower, or the tank is empty, I want the pump to start filling the tank.
When the level is 0 my pump works with 5V, and at 75% full tank it stops. This is OK. But...
2. When I put AC0 at 16000 (50% of full tank) my pump works at around 3.5V. My water level stays the same, I don't change AC0 (like the water is going out at the same rate). I aspect the PLC to TRY to fill the tank up to 75% and therefore INCREASE the pump voltage. But it stays the same?!? Why is that?
3. When I start PID Tune Control Panel I can monitor values in the process, but when I try to start AutoTune I get error: 'The tuning algorithm was aborted due to the process going out of range'.
I tied changing the Gain and Integral Time, but no luck.
It would help me A LOT if You could send me a simple ladder program block with PID done with PID Wizard (if You have one for problem similar to mine even better), because I couldn't find any, not on net or with Siemens. Everything I found on Your forum is to theoretical. The examples in the Siemens tutorial like: 'tip53.mwp' on How to Use the PID Instruction Wizard and 'tip54.mwp' on How to Use the PID Loop Instruction are done in a different way, I think. They explain what goes on inside PID loop, but are not generated by PID Wizard, and therefore I can not use them to solve my problem.
I have been working on this for 2 weeks now, and read and studied everything I could find, but no luck. I am sorry for such a long post, I just wanted to be clear about what I was doing (or TRYING to do).
[HIGHLIGHT]You're my last resort![/HIGHLIGHT] Thanx in advance.
 

Similar Topics

Hello everyone, I'm new in using plc software. I want to set a parameter for my centrifugal pump using an i/p from PID block so that the range of...
Replies
0
Views
1,272
Anyone have any experience with the PID control on siemens S7-200 PLC? I am planning to implement it on two new systems - temperature control and...
Replies
1
Views
3,910
Hi everyone, I am trying to use a Siemens S7 315-2 PLC to do level control. I have been getting some help from this site and have some of it...
Replies
6
Views
12,777
Hi everyone, I want to upload the program from my CPU317TF-2 DP to my PC via connecting to CP 343-1 Advanced since it has LAN ports and the CPU...
Replies
1
Views
123
Buona sera, Ho dei problemi nell' interfacciare PLC S5 con HMI 2a Gen. Siemens (ad esempio KTP400) tramite IBH Link S5++. il mio obbiettivo è solo...
Replies
0
Views
63
Back
Top Bottom